The brain consists of a vast network of neurons that communicate with each other via chemical messengers. Each neuron generates neurochemicals or neurotransmitters which act at sites referred to as receptors on the cellular membranes of neurons. One group of neurotransmitters, referred to as the monoamine neurotransmitters, includes serotonin, dopamine and noradrenaline. Monoamine neurotransmitters are released into the synaptic cleft between neurons in order to stimulate post-synaptic receptor activity. The removal (or inactivation) of monoamine neurotransmitters occurs mainly by a reuptake mechanism into the pre-synaptic terminals. By inhibiting the reuptake, an enhancement of the physiological activity of monoamine transmitters occurs.
The serotonergic neural system of the brain has been shown to influence a variety of physiologic functions, and compounds having dopamine reuptake-inhibiting activity have been shown to have the ability to treat in mammals, including humans, a variety of disorders associated with this neural system, for example, eating disorders, depression, cocaine addiction, dementia of aging, memory dysfunction in aging, and attention deficit hyperactivity disorder.
However, the use of dopamine transport inhibitors to treat such conditions frequently brings along with it a number of undesirable side effects. For example, benztropine (COGENTIN™) is a high affinity dopamine transport (DAT) inhibitor that increases dopamine activity in the brain. This material has been in continuous clinical use for over forty years. Benztropine's inhibition of the dopamine transporter is responsible for its clinical effectiveness for treating idiopathic Parkinson's disease, a clinical indication for which it is FDA approved. Unfortunately, the clinical usefulness of benztropine has been severely limited by its anticholinergic properties which result from benztropine's high affinity binding to M1 cholinergic receptors. Benztropine's anticholinergic side effects, as documented in the Physician's Desk Reference, include tachycardia, constipation, vomiting, confusion, disorientation, memory impairment and hallucinations.
The present invention provides the therapeutic benefits of dopamine transport inhibitors while demonstrating low affinity for M1 cholinergic receptors. The compounds described herein, therefore, retain benztropine's clinical utility for treating disorders associated with dopamine insufficiency in the brain while demonstrating reduced anticholinergic side effects due to limited M1 cholinergic binding.
U.S. Pat. No. 5,792,775, Newman, et al., issued Aug. 11, 1998, describes the family of 4′,4″-substituted 3α-(diphenylmethoxy) tropane analogs utilized in the present invention and teaches their use for the treatment of cocaine addiction and for the diagnosis and/or monitoring (but not the treatment of) neurodegenerative disorders, such as Parkinson's disease.